Pulse oximetry is a non-invasive procedure for determining physiological parameters, such as an oxygen saturation level of arterial blood, pulse rate or the like, by processing received light-energy emissions after they have been attenuated by tissue at a measurement site. Generally, pulse oximetry involves an optical probe or sensor comprising one or more emitters, such as light emitting diodes (LEDs), and a photodetector (detector). The LEDs and detector are positioned in proximity with the patients skin. The LEDs emit light energy at predetermined wavelengths which transmits through the patient's tissue, is attenuated thereby, and is detected by the detector. A signal representative of the detected attenuated light energy is then passed through electrical communication to a monitor, such as a pulse oximeter, which processes the signal and determines one or more physiological parameters of the tissue at the measurement site.
Optical probes are generally applied to the measurement site in at least several distinctive manners. For example, one application positions the emitters on a side of the measurement site opposite the detector such that the light energy passes from one side of the measurement site, through the tissue, and to the detector positioned on the other side of the measurement site. Another reflective-type application positions the emitter and detector generally proximate one another on the same side of the measurement site. Drawbacks arise in reflectance-type sensors when light energy from the LEDs bounces along the surface of the tissue at the measurement site, or otherwise reaches the detector without passing through the tissue. Such light energy has not been attenuated by the tissue, and therefore, distorts or otherwise provides noise to the energy being received at the detector.
Additionally, reflectance-type sensors present various drawbacks during application, such as, for example, improper positioning on a measurement site, improper securement to the same, or the like. These drawbacks can increase the likelihood that light energy reaches the detector without having first been attenuated by the tissue.
Monitoring systems can also present drawbacks of backwards compatibility when dealing with newly developed sensor technologies. For example, pulse oximeters generally include sets of calibration curves used to associate data received from the detector with values of data used to determine the physiological parameters or the parameters themselves. Thus, as new sensors are developed and used during patient monitoring, the oximeter may not include an appropriate set of calibration curves to appropriately associate detected energy with the foregoing data.
Embodiments of the present invention seek to overcome some or all of these and other problems.